Isaiah’s “there is no other” passages are the strongest anti-Trinitarian texts in the Bible. God speaks as a single “I” with no hint of three persons.

These passages rule out three gods, and they are presented here as the constraint the Trinity must satisfy, not as evidence for it. The Trinitarian reply is that these same chapters are the ones the New Testament most often applies to Jesus: Isaiah 45:23’s every knee shall bow is applied to Jesus in Philippians 2, and Isaiah 44:6’s first and last is claimed by Jesus in Revelation. Whoever wrote those New Testament passages knew Isaiah’s exclusivity language well and still placed Jesus inside it. That is the puzzle the doctrine exists to solve.